It is standard to package smelting additives in a strand or wire so that the strand can be measured out and added to the molten charge being smelted. The filiform shape makes the material melt and mix well with the molten charge. It also facilitates measuring the chemicals since the content for a given unit of length is known, and deriving a given quantity is simply a method of dividing the quantity needed by the content per unit of length to obtain the length of the piece to be added to the melt.
The strand is formed of an outer skin shaped out of thin mild-steel strip stapled into a tubular shape and a core filled with a granular or pulverent dry particulate. The skin normally is about 0.4 mm thick for standard filled wire having a large diameter of 13 mm or 18 mm, but is only about 0.2 mm thick for thinner filled wires having a small diameter of 5 mm, 7 mm, or 9 mm. The additive core of the strand is typically aluminum, calcium, nickel, titanium, or alloys such as SiCa, SiCaBa, and SiZr, and serves to increase the deoxidation/desulfurization effectiveness of an alloying operation. Regardless of size, such a wire is a stiff and heavy item that is nonetheless relatively fragile.
The wire must be packaged so that an automatic apparatus can pay it out automatically at a high or low speed and so that it can stop the advance of the wire surely, all without damaging it. Hence it is standard to wind the wire up on wide-flange spools that can hold it in a neatly coiled toroidal shape centered on the axis of the spool. Such spools must be very robust due to the density and fragility of the strand. They are made of wood, sheet metal, or of heavy wire and normally form when full a package having an overall weight of a ton for large-diameter wire or about 150 kg for small-diameter wire.
Such a spool is normally mounted on a shaft for rotation about a horizontal axis by an automatic apparatus which pulls off the desired quantity of wire. This device comprises a brake for the spool so that when the desired quantity of wire has been payed out, the spool's rotation can be stopped. For accurate dosing of the additive it is therefore necessary to control the equipment that pays out and cuts off the payed-out strand very accurately, so that the spool rotation must be stopped rapidly. The rotation speed of the spool must be fairly high for efficient operation, so that the starting and stopping of the rotation of the wire-carrying spool is fairly abrupt.
Since a small 150 kg spool can be used up in two batches, it is standard nowadays to use the larger spools weighing about 1 ton. This increase in size increases the problems of handling the wire. As a result rupture of the fairly fragile wire is common.
It has therefore been suggested to set the spool on its end and to pull the wire axially up off it, without letting the spool rotate. This solution obviously reduces the above-discussed drive problems. Nonetheless, for each turn of the coil that is pulled off the spool the wire is twisted one turn on itself, something that normally does not excessively strain the wire at high speeds.
The turns of the wire that are pulled off from immediately adjacent the upper flange of the spool are subjected to considerable abrasion as they pass radially out and then bend axially up past the edge of this flange. Since the wire is being twisted at the same time as it is being scraped over this edge, chances of breakage are considerable. Thus it is known to mount a guide eye on the outer end of an arm having an inner end pivoted at the spool axis, so that engagement of the wire with the upper spool flange is avoided. Such structure, however, is relatively complex and frequently the wire jumps out of the eye when the wire starts or stops.
In the wire-feeding art it is known, for instance from U.S. Pat. No. 2,935,274 of Pearson to provide a fitting which sits atop a standard spool of wire and which carries a ring that is held so that it lies below the upper flange of the spool. Thus the wire can be pulled generally tangentially off the spool, then axially up and over the ring so that it does not contact the rough spool edge. Such an arrangement relies on contact between the wire and a stationary object in passing the wire out and then in over this ring, and can damage a powder-filled wire of the type the instant invention is aimed at feeding.
Similarly, in U.S. Pat. No. 3,434,677 an arrangement is provided which has a ring like that of the Pearson system, but set up so as to rotate about the spool axis, and carrying two angularly oppositely directed guide sheaves. The wire that is payed off the spool catches in one or the other sheaves, depending on the direction it is moving in, and then can roll up and out. Although such an arrangement is fairly gentle, it is a fairly complex piece of equipment which is used with different spools. Thus the spools must be loaded into the unwinding device so that setup time is considerable.
In the textile arts guide rings are also known. For instance in U.S. Pat. No. 2,650,042 of Markwood a ring is shown having a pinch arrangement that catches and breaks a yarn moving in the wrong direction. Otherwise this system has a stationary ring like the Pearson device. Similarly, in U.S. Pat. No. 2,723,809 of Vanderspek a loose skein of yarn is held in a device which pulls the yarn over a stationary ring, then axially through the center of the skein and radially away. Such a system would be unworkable with a heavy filament such as the one the instant invention deals with.
Another problem faced by a filled strand is that the turns of the coil tend to stick together somewhat. The individual turns are very massive and are often used in somewhat dirty environments, so that they can adhere to one another in part from the effects of rust and in part just because the soft strand compacts together somewhat. Thus when unwinding it is necessary to separate the turns from one another rather carefully, but gently, to prevent several turns from catching together, kinking, and jamming the machine.